A piezoelectric ceramic composition is nowadays used for an electromechanical transformation device such as actuators, ultrasonic-sensors, ultrasonic-transducers or the like. A piezoelectric-ceramic composition showing an excellent piezoelectric property contains a lead compound such as lead zirconate titanate (PZT) or the like. However, that is a cause for concern regarding the negative affect that it has on the environment. Therefore, a piezoelectric-ceramic composition that is free of such a lead-compound is now attracting attention and is being researched and developed. As disclosed below in Patent Reference One, the potassium-sodium-niobate-system piezoelectric-ceramic composition is just such a composition that is free of lead and yet has an excellent piezoelectric property of a relatively high electromechanical-coupling coefficient as well as a relatively high Curie temperature Tc, so that it can appropriately be used under high temperatures.
The type of piezoelectric-ceramic composition showing an excellent piezoelectric property that is nowadays used in the making of electromechanical-transformation devices such as actuators, ultrasonic-sensors, ultrasonic-transducers or the like contains a lead compound such as lead zirconate titanate (PZT) or the like. However, that type of piezoelectric-ceramic composition is a cause for concern regarding the negative affect that it has on the environment. Therefore, a piezoelectric-ceramic composition that is free of such a lead compound is now attracting attention and is being researched and developed. As disclosed below, in Patent Reference One, the potassium-sodium-niobate-system piezoelectric-ceramic composition is just such a composition that is free of lead and yet has an excellent piezoelectric property of a relatively high electromechanical-coupling coefficient, as well as a relatively high Curie temperature Tc, so that said composition can appropriately be used under high temperatures.
The potassium-sodium-niobate-system piezoelectric-ceramic composition incorporates a crystalline-phase of a perovskite structure that is shown as composition-formula ABO3. Although the perovskite structure depends on this type of composition, the piezoelectric-ceramic composition incorporating the potassium-sodium-niobate-system material reveals the tetragonal-to-cubic-phase transition temperature Tc to be about 300 to 400 degrees Celsius and the orthorhombic-to-tetragonal-phase transition temperature To-t to be about −30 degrees to +100 degrees Celsius. If such a piezoelectric-ceramic composition is used in the making of an electromechanical-transformation device, then polarization is typically done by applying a high electric field within the temperature-range required to form the tetragonal-crystal to get the piezoelectric property.